Download Mitosis Lecture and Lesson

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Mitosis Summary
Name ___________________
Date 11/17 Period______
When humans are conceived, they are simply a single-cell organism. Eventually, they grow to become a larger, many
celled organism. How does this happen? How does our one-cell self become a living, breathing being made up of billions
and billions of cells? The way this happens is through the cell cycle. The cell cycle is where one cell, called the parent
cell, divides in half to produce two daughter cells which are identical to the parent cell and to each other.
1.
What process allows people to grow from single-cell organisms to full sized adults?_________________
2. Where do new cells come from? __________________________________
3. How many daughter cells are created when one parent cell divides?____________
4. How are the daughter cells related to the parent?_________________________________________
There are several reasons that cell division needs to happen. First, cells need to divide so that we can grow. Many
organisms and structures grow through cell division (babies, plants, tadpoles, fingernails). Second, cells need to divide
as a method of repair (broken bones, bruises, lacerations). The third reason cells divide is to replace dying cells. Your
skin is constantly dying and sloughing off of your body. Most of the dust in your bathroom is made up of dead skin cells.
If these cells didn’t constantly divide and replace themselves, you would have no skin. Blood cells also need to be
constantly replaced because they have an average life span of two days. (To reproduce the use meiosis. During meisois the
chromosome number is reduced by half and they create four daughter cells instead to two. The daughter cells are all different)
5. Name three reasons for cell division. ________________, _______________, ________________
6. What would happen if your skin cells didn’t constantly divide?__________________________________
Most cells have a nucleus filled with DNA in strands. These cells use the cell cycle to divide. In the cell cycle, a parent
cell splits into two identical daughter cells, each containing a full and identical set of DNA. To understand the cell
cycle, you must be familiar with the different ways DNA can be arranged. DNA is the genetic material found in the
nucleus of a cell which carries instructions for making proteins. The entire length of DNA is divided into sections
called chromosomes, kind of like a textbook is divided into chapters. Each chromosome contains information for
certain traits/characteristics (like our textbook chapters contain information about specific topics).
7. Where is DNA found? _______________________
8. What is a chromosome?_______________________________________
Just as people spend a lot of time sleeping and relaxing, the cell spends most of its time in a relaxed
state. In this state, the DNA in the nucleus is a tangled mess that looks like a bolt of yarn that is
unwound. When the cell starts to divide, the DNA coils up and looks like that has been wound on the
yarn bolt. This condensed DNA is called chromosomes, and is found in the dividing cell.
Chromosome
9. What happens to the DNA when the cell starts to divide? _______________________
10. Draw a chromosome to the right
Chromosomes can come in two forms. A single, un-replicated chromosome is represents one copy of a section of DNA
and looks like a single strand. Before the cell divides, it must make a complete copy of each chromosome. Each
chromosome is copied and the two copies remain attached to each other like identical Siamese twins. Both the single
chromosome strand and the two attached strands are considered to be one chromosome.
11. What is a chromosome?_____________________________________
12. What are the three forms that DNA and chromosomes can take?
______________________, __________________________, __________________
The Cell Cycle has three parts: Interphase, Mitosis, and Cytokinesis.
Interphase: Before the cell cycle begins, the cell must make a copy of its DNA. Replicating the DNA allows a full copy
of DNA to go into each daughter cell. Interphase, the first stage of the cell cycle, is where the replication of DNA
occurs. In interphase, the DNA in the nucleus is all tangled because the cell is relaxed called chromatin.
13. What does the DNA look like during interphase?_____________________________
14. What are the three stages of the cell cycle? _____________________, ______________________,
_____________________________
15. What must happen to the cell before it can divide?__________________________________________
16. What happens to the DNA during interphase?_____________________________________________
Mitosis: The second stage of the cell cycle is mitosis. Mitosis is simply the division of the nucleus and everything in it.
In mitosis, one nucleus with DNA becomes two nuclei with DNA. The two attached chromosome copies are split so that
one of each goes into a different cell.
17. What happens during mitosis?____________________________________
18. What happens to the attached chromosome copies during mitosis? _______________
The process of mitosis consists of four stages of its own. The four stages can be remembered with the letters: PMAT. The
stages are prophase, metaphase, anaphase, and telophase. To understand these stages, you must understand what
centrioles and spindle fibers are. Centrioles are small organelles found only in animal cells which help the cell to divide. They
are like little fishermen standing on the edge of a lake holding a rod and reel. Spindle fibers are fibers which grow from the
centrioles and attach to the chromosomes. They are like the line in the fishing reel. When we talk about mitosis, we will refer
to the cell as if it were a globe. The poles are the outer edges (opposite from one another) and the equator runs through the
center.
19. What does PMAT stand for? ______________________________________________________
20. Do the PMAT stages occur during interphase, mitosis, or cytokinesis? ____________________
21. What is the function of centrioles?____________________________________________________
22. What kind of cell are centrioles found in? ________________________________________________
23. What do spindle fibers attach to during mitosis? _______________________________
In prophase, the nucleus that holds the DNA disappears and the DNA coils up into chromosome strands. The centrioles and
spindle moves to the poles of the cell. The cell is getting ready to start the division process. The centrioles are like
fishermen on opposite sides of a lake, and are casting out their lines (spindle) to catch a fish (the chromosomes).
24. What happens in prophase? _______________________________________________________
25. What is the cell preparing for? ____________________________________________________
In Metaphase, the chromosomes will line up single file on the equator. The spindle attaches to each chromosome from each
pole. This means that each fisherman (the centrioles) have hooked each fish (the chromosomes) with their fishing lines
(spindle).
26. What two things happen in metaphase? _________________________________________________
27. What phase comes after prophase? _________________________
In Anaphase, the spindle shortens (like the line of the rod and reel will shorten when the fisherman is reeling it in), and
the chromosomes are pulled in two different directions. Eventually, the pressure from each side will cause the
chromosomes to split apart and one copy of each chromosome will be pulled to each side of the cell.
28. What happens to the chromosomes and their attached copies in anaphase?
29. Why do the chromosomes tear apart?
30. Where do the chromosome copies end up?
In the last phase, telophase, everything that happened in prophase is reversed. The nucleus comes back, the spindle
disappears, the centrioles leave the poles, and the chromosomes relax into chromatin again. There is now one cell with
two nuclei and each nucleus has a full set of DNA.
31. What phase is the opposite of telophase?
32. What happens in telophase?
Cytokinesis: The third main part of the cell cycle is cytokinesis. After the completion of mitosis, cytokinesis begins and the
entire cell splits into two identical daughter cells, each with its own nucleus and its own full set of DNA. In the animal cell, a
cleavage furrow forms in the center of the cell, and allows the cell to pinch in half. In plant cells, a cell plate and then a cell
wall grows between the two halves of the cell.
33. What is the main thing that happens in cytokinesis? _______________________________________
34. How does the plant cell divide? ___________________________________
35. What is a cleavage furrow, and what kind of cell is it found in? _________________________________
36. How does the animal cell divide? _________________________________
*****The best way to remember the three stages of the cell cycle is:

Interphase – growth and replication

Mitosis – nucleus divides:

Prophase: nucleus disappears, chromosomes condense, centrioles move to poles

Metaphase: chromosomes line up at the equator and spindle fibers attach

Anaphase: spindle shortens, splitting chromosomes and pulling half to each pole

Telophase: nucleus forms around the chromosomes in each half of the cell

Cytokinesis – cell splits
Meiosis
Human DNA is the material which tells the cells how to make protein. All of the DNA in a cell is
divided into little strands called chromosomes. Each chromosome holds a portion of the cell’s
DNA. In humans, we have 46 chromosomes. Each chromosome is divided into genes. One gene
codes for one trait. To the right is a picture of a chromosome divided into genes. A gene may
control the color of hair, whether or not you are double jointed, cleft chin, hitchhiker’s thumb,
widow’s peak.
1. What is the function of DNA?
2. What is DNA divided into?
3. How many chromosomes do people have?
4. What smaller unit are chromosomes divided into?
5. What do genes give instructions for?
Chromosomes in the nucleus are arranged in pairs. These pairs are called homologous pairs. One chromosome in each
pair comes from mom, the other comes from dad. In humans, we have 23 pairs of chromosomes,
with one chromosome in each pair coming from the mom, and one coming from the dad (like if 23
students took off their shoes and threw them into a pile, there would be 46 shoes, or 23 pairs of
shoes in the pile – one shoe will come from the left foot and one from the right foot). Each
chromosome in the homologous pair has the same genes (like the two homologous shoes have the
same logo, size, color….). For example, each of the two chromosomes in a homologous pair may
have genes for widow’s peak, eye color, diabetes, and hand preference.
6. What is a homologous pair?
7. Homologous chromosomes are alike because they have the same _______.
8. Where does each chromosome in a homologous pair come from?
9. How many homologous pairs do people have?
There are two kinds of cells in the body. There are the normal body cells, called somatic cells, or body cells. Then
there are the sex cells – sperm and egg. These cells are called gametes. Regular cells in the body are found everywhere
except for the ovaries and testicles and include all kinds of cells except for sperm and eggs. Muscle cells, blood cells,
liver cells are all body (somatic) cells. Somatic cells are diploid. Diploid cells are ones that have homologous pairs of
chromosomes – one from mom and one from dad. Somatic cells are formed through mitosis.
10. What are the two kinds of cells found in the body?
11. What are gametes?
12. What are the two kinds of gametes?
13. Name three kinds of body cells
14. What is meant by “diploid?”
15. What type of cells are diploid?
Sex cells (sperm and egg) are called gametes, and are made in the ovaries of women and the testicles of men. Gametes
are haploid – they do not have homologous pairs. Human gametes have ½ the number of chromosomes as body cells,
because they only have one chromosome from each pair (like if 23 students only took off one shoe from either their
left or their right foot and tossed it into the pile) Haploid cells that have half of each chromosome pair are formed
through meiosis.
16. Where are gametes made?
17. What is meant by haploid?
18. How are gametes made?
19. If a cell has homologous pairs, is it haploid or diploid?
Remember that mitosis is the way somatic (body) cells in the body divide to help the body grow, repair damaged cells
and replace dead cells. In mitosis, a diploid parent cell, the cell that divides, produces two diploid daughter cells which
are identical to it and to each other. The daughter cells have the exact same set of DNA and chromosomes as the
parent. All the cells in the body divide by the process of mitosis except for one type of cell – the egg and sperm cell
(gametes). The gametes reproduce by a process called meiosis.
20. In mitosis, how many daughter cells are produced from a single parent cell?
21. What kind of cells are made through mitosis?
22. How are the daughter cells related to the parent in mitosis?
23. How are sperm and egg cells made?
Meiosis is like mitosis, but with some differences. Meiosis involves two sets of divisions (the nucleus and DNA divides
twice), producing four daughter cells from one parent cell. Because it divides twice,
each daughter cell will have half the number of chromosomes as the parent cell. If the
cell begins with 46 chromosomes, or 23 pairs, it will end with 23 chromosomes - one
from each pair. Another thing that happens at the beginning of meiosis is that
homologous chromosomes move very close together. When they do this, sometimes they
exchange genes. This means that some of the mom’s genes will now be on the dad’s
chromosome, and some of dad’s genes will be on the mom’s chromosome. This process of
swapping material from one chromosome to another during meiosis is called crossing
over. At the end of meiosis, the one diploid parent cell has created four daughter cells,
all different from each other and from the parent. There are no homologous
chromosomes because the homologous pairs are split into separate cells. The gametes
are haploid.
24. What kinds of cells are created in meiosis?
25. How many times does the cell divide in meiosis?
26. How many daughter cells are created from each parent?
27. What is crossing over?
28. How are the chromosomes different after crossing over than they were before it?
29. How are the daughter cells in meiosis different from the daughter cells in mitosis (name three ways)?
Meiosis is important for two reasons. First, is cuts the number of chromosomes within a cell in half, allowing
gametes to have half the number of chromosomes as normal body cells. This way, when the sperm (23
chromosomes) and egg (23 chromosomes) combine during fertilization, the new baby will have the correct total
number of chromosomes in all its body cells (46 chromosomes – 23 pairs). The other important thing to
remember about meiosis is that it produces genetic variability – new combinations of genes. Because of meiosis,
all organisms are different and unique. The main source of variability and unique combinations of traits during
meiosis comes during crossing over.
30. What are the two most important thing about meiosis?
31. What would happen to the number of chromosomes in a baby's cells if gametes were diploid instead of
haploid?